Narrowband PLC and the power line medium

IntroductionThe introduction of the Smart Grid on a mass scale requires robust and reliable communication services. In general, a combination of two communication systems is taking on the challenge: short range or mesh wireless and narrowband power line communication (N-PLC). Both systems face challenges when millions of devices send and receive information and each of them has its place in various deployment environments and regional regulatory climates.

The idea of using the AC mains for communications is not new. The concept of sending communication signals on the same pair of wires that are used for power distribution dates to patents from 1924 implementing "Carrier Transmission Over Power Circuits”. The simple carrier signaling evolved to using various modulation schemes that comprise N-PLC. Only in the last two decades, however, advancements in communications technology made N-PLC a commercially viable solution for large scale deployments.

Narrowband power line Communication (N-PLC) is generally defined as communication over power line that is typically operating in transmission frequencies of up to 500 kHz (as opposed to Broadband PLC that targets much higher bandwidth at shorter distances and operates over a much higher frequency band). Specifically, frequencies of 148.5 kHz and less have been recognized by Europe's CENELEC standards bodyfor use in N-PLC systems on a public utility’s power wires. Within this frequency range the resulting data rates are modest, ranging from 1Kbps to less than 100Kbps. These rates are appropriate for telemetry and control applications. In North America, Japan and China, the frequency range of up to 500 kHz are viable under local regulations for N-PLC and offers a reasonably wide communications bandwidth (up to above 300Kbps) and a broader range of applications can be considered.

In a power transmission and distribution system the conduit available to all nodes by definition is the power line. An N-PLC system that can provide reliable and cost effective data communication capabilities is an ideal and natural solution to grid communication needs. However, due to the characteristics of the power line noise environment, its changing conditions and variations in equipment and standards, communications over the power grid are difficult. To both reliably operate in this challenging environment and to successfully co-exist with previously installed equipment requires new approaches. This article focuses on the characteristics of PLC within this frequency range and presents the common communication techniques currently used within this band.

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It certainly is true that implementing a successful PLC system is a challenge, but the same can be said for wireless: meters are often installed in unfavourable locations like basements and in most of the world outside the US, houses are built using solid materials like stone or concrete which are far from transparant for radio waves. Using PLC is very attractive for grid operators as this is the only solution offering plug&play: you connect the meter to the LV-network and at the same time it can contact its concentrator. Noise and variable impedances at PLC-frequencies is a real and tough problem however and one can say that in the future one can only expect the number of noise sources in appliances to further increase (electronic ballasts for energy efficient lighting, Photo-voltaic convertors, electric cars, ...). We at Eandis have developed a solution for these problems: our patented technology uses filters to isolate the customers' LV-loads from the outside grid and we decided to use multiple gateways on each network segment to further increase reliability of the powerline communication. It's implemented in a test area with about 3000 customers and we are able to consistently read out over 95 % of the meters every hour and over 99% daily. In fact we had more issues with the firmware and software than with the PLC. By using multiple gateways we get a bandwidth of up to 9.6 kbps per 10 connected meters average, which we consider sufficient to be able to support IP over PLC in the future.

I am not ready to say narrowband PLC has out-lived its usefulness. The early implementations were really for fault detection in power transmission (though there were challenges to 'jump' across transformers) and the repair. From the utility provider's point of view, this was and still is a necessary piece of the communication needed in a system, even if it ends up being a backup/redundant.
MP Divakar

Narrow band communication over power lines certainly would face a few challenges, but not the legal ones that broadband faced, caused by it's interference generation. The reason for seeking narrow band communication in some areas is because there is no internet there, so the assertion that internet is a better choice is sort of not the issue. It is possible that other methods might be better, but the questions about relative cost and reliability need to be answered in detail before that call can be made correctly. Glittering generalities have no place in the decision making process, only actual data.

PLC from a technology point of view isn't useless at all. It depends on the application but obviously there is not a single technology that fits all.
Even if get closer to standards on communications providing solutions for a wide range of scenarios, some special cases will always have their own rules.
Coming up with business models generating revenue with PLC isn't that easy but also a complete different story.
Research in PLC has brought up good results which diffused to other areas too. In some parts of the world PLC is used successfully. Beside that technology in general provides diversity in people's life and business. PLC is one of it.

The author sumarizes: "power line as communications medium presets unique challenges."
An understatement, to say the least.
The entire concept of PLC makes no sense, either from an engineering or business perspective. And I think you have to state your objective, in analyzing any proposal.
IF you want to enable remote or automatic meter reading, to save utilities labor expense-- forget about power comms--use available wideband--and either provide consumers a discount for automatic reading, or cut a deal with cable companies or cellphone carriers, for data backhaul from a smart meter.
IF you want to provide realtime command and control of the national grid, to provide smart power routing, and source switching, to match peak demand and alternative source variabiity, you need an agile wideband system which is separate from the network you want to control. And we've already got that over 95% of the US, with the internet.
From an investment standpoint, as well as a communications engineering perspective, PLC is a technology which offers nothing.
The only reason it's still around is the relative expense of wideband (way down from where it was 20 years ago, and falling) versus sunk cost in the existing utilities outside plant.
Overlay divested power generation and distribution companies on that backdrop, and it makes even less sense.
It's time for a national energy vision, and a policy for implementation. We're wasting time on PLC.